The invention relates to Medium Access Control (MAC) protocols in CSMA networks.
A protocol known as the Automatic Repeat request (ARQ) protocol may be defined as any protocol that uses positive or negative acknowledgments with retransmission techniques to ensure reliability. A transmitting station automatically repeats a transmission if it receives a negative acknowledgment or no response at all when a response was expected. Standard ARQ schemes can be used by unicast transmissions that involve only one destination and thus one response. Typically, transmissions involving more than one destination, such as multicast and broadcast transmissions, do not use standard ARQ mechanisms because the medium would be flooded with response-related traffic, causing overall network performance to suffer.
In one aspect of the invention, operating in a network of devices connected to a shared transmission medium includes selecting one of the devices and indicating in a frame to be transmitted onto the shared medium in the frame transmission to intended recipients that a response is expected and that the selected device is to provide the response.
Embodiments of the invention may include one or more of the following features.
Selecting can include selecting the device from among those of the devices that correspond to the intended recipients. Indicating can include specifying in the frame an address of the selected device as a destination address. Indicating can further include a multicast flag for indicating that the frame transmission is intended for more than one recipient. Indicating can further include MAC management information for indicating actual destination addresses of the intended recipients of the frame transmission. Indicating can further include MAC management information for indicating a group address associated with the actual destination addresses of the intended recipients of the frame transmission.
The frame transmission may be a multicast transmission.
The frame transmission may be a broadcast transmission.
The selected device can be a station or, alternatively, a bridge.
Selecting can include identifying which of the devices is least likely to receive the frame transmission. Identifying can include using channel maps for the devices to determine which of the channel maps supports a lowest data rate.
Alternatively, selecting can include selecting the proxy in a random manner.
Among the advantages of the present invention are the following. The xe2x80x9cpartial ARQxe2x80x9d mechanism increases reliability of a multicast or broadcast transmission at the MAC. It allows one member of a group of intended recipients, or, alternatively, any device connected to the same network medium, to acknowledge a transmission directed to the group of intended recipients as a proxy for the group. Although partial ARQ does not guarantee delivery to the entire group, it provides an indication that the transmission was received by at least one device on the same network. The proxy can be chosen as the device least likely to receive the transmission (and therefore representing the worst-case transmission path), thus improving reliability of the partial ARQ mechanism itself.
Other features and advantages of the invention will be apparent from the following detailed description and from the claims.